1. Field of the Invention
The present invention generally relates to reducing vertical segregation in a high intensity discharge (HID) lamp. The present invention specifically relates to reducing vertical segregation by an excitation of an azimuthal acoustic and longitudinal acoustic combination mode of the HID lamp.
2. Description of the Related Art
Acoustic resonances are driven by a periodic power input. For sinusoidal type waveforms, the power frequency that excites an acoustic resonance is at twice the current frequency.
A reduction of vertical segregation (color mixing) in a HID lamp has previously been accomplished by exciting the 2nd longitudinal acoustic mode of the lamp. For, a long and thin burner, the frequency to excite the 2nd longitudinal acoustic mode of the HID lamp is lower than both the frequency to excite the 1 st azimuthal acoustic mode of the HID lamp and the frequency to excite the 1st radial acoustic mode of the HID lamp. Prior to exciting the 2nd longitudinal acoustic mode of the HID lamp, the HID lamp is initially stabilized by repeatedly sweeping a current frequency signal over a frequency range extending between a current frequency corresponding to the 1st azimuthal acoustic mode of the HID lamp and a current frequency corresponding to the 1st radial acoustic mode of the HID lamp.
For example, for a 70 watt HID lamp having a 4 millimeter inner diameter and a 19 millimeter inner length, the current frequency and the power frequency corresponding to the 1st azimuthal acoustic mode of the 70 watt HID lamp is 31.5 kilohertz and 63 kilohertz, respectively, and the current frequency and the power frequency corresponding to the 1st radial acoustic mode of the 70 watt HID lamp is 65.5 kilohertz and 131 kilohertz, respectively. One prior art method for initially stabilizing the 70 watt HID lamp sweeps the current frequency signal from approximately 45 kilohertz to 55 kilohertz every 10 milliseconds within an initial operating time period.
Upon an expiration of the initial operating time period, one prior art method for exciting the 2nd longitudinal acoustic mode of the 70 watt HID lamp utilizes an amplitude modulation of the current frequency sweep signal. The current frequency and the power frequency corresponding to the 2nd longitudinal acoustic mode of the 70-watt HID lamp are 12 kilohertz and 24 kilohertz, respectively. The resulting power frequencies are a power frequency sweep with 2 swept sidebands and a fixed power frequency at the amplitude modulation frequency, which is adjusted to correspond to the power frequency of 24 kilohertz to excite the 2nd longitudinal acoustic mode of the 70 watt HID lamp. A potential problem however with this prior art method is the required complexity of a circuit to implement the method.
Another prior art method cycles a current frequency sweep signal of 45 kilohertz to 55 kilohertz for a first time period followed by a fixed current frequency signal of 12 kilohertz for a second time period. The resulting power frequencies are a power frequency sweep of 90 kilohertz to 110 kilohertz during the first time period of each cycle and a fixed power frequency of 24 kilohertz during the second time period of each cycle. A potential problem however with this prior art method is also the required complexity of a circuit to implement the method.
In particular, one prior art circuit includes a bridge for cyclically generating a current frequency sweep signal in the form of a square wave at 45 kilohertz to 55 kilohertz for the first time period of each cycle and a fixed current frequency signal in the form of a square wave at 12 kilohertz for the second time period of each cycle. The circuit preferably includes a low pass filter for transforming the square waves to sine waves by attenuating the 3rd harmonic, the 5th harmonic and higher harmonics of the square waves. While the low pass filter passes the fundamental current frequency sweep signal of 45 kilohertz to 55 kilohertz without any appreciable attenuation during the first time period of each cycle, the low pass filter fails to attenuate the 3rd harmonic at 36 kilohertz and the 5th harmonic at 60 kilohertz of the fixed current frequency signal of 12 kilohertz during the second time period of each cycle. The result is the 70 watt HID lamp receives a fixed current frequency signal of 12 kilohertz having a square wave during the second time period of each cycle that fails to excite the 2nd longitudinal acoustic mode of the 70 watt HID lamp. A higher order filter, or a phase modulation can overcome the shortcomings of the low pass filter, but at an increase to the complexity of the circuit.
Color mixing results in light technical properties of long and thin lamps being approximately equal in a vertical orientation and a horizontal orientation. Color mixing can also significantly reduce the color temperature or increase the efficacy in vertical orientation. It is therefore desirable to provide a method and system for achieving color mixing with a circuit having a less complex design than prior art circuits.
The present invention relates to a method and system for exciting an azimuthal acoustic and longitudinal acoustic combination mode of a high intensity discharge lamp. Various aspects of the invention are novel, non-obvious, and provide various advantages. While the actual nature of the present invention covered herein can only be determined with reference to the claims appended hereto, certain features, which are characteristic of the embodiments disclosed herein, are described briefly as follows.
A first form of the present invention is a power source system for reducing vertical segregation in a high intensity discharge lamp. The system comprises a power source and a controller. The power source is operable to provide a current frequency signal to the lamp to excite an azimuthal acoustic and longitudinal acoustic combination mode of the lamp. The controller is operable to control the current frequency signal to stabilize a reduction in vertical segregation within the lamp.
A second form of the present invention is a first power source for reducing vertical segregation in a high intensity discharge lamp. The power source comprises a bridge and a low pass filter. The bridge is operable to provide a first current frequency sweep signal in the form of a square wave. In response to the first current frequency sweep signal, the low pass filter is operable to provide a second current frequency sweep signal in the form of a sine wave to the lamp, wherein the second current frequency sweep signal has a frequency range to excite an azimuthal acoustic and longitudinal acoustic combination mode of the lamp.
A third form of the present invention is a second power source for reducing vertical segregation in a high intensity discharge lamp. The power source comprises a pair of signal generators and an adder. The first signal generator is operable to provide a fixed current frequency signal. The second signal generator is operable to provide a current frequency sweep signal. The adder is operable to provide a current frequency signal as a function of the fixed current frequency signal and the current frequency sweep signal to the lamp, wherein the current frequency signal excites an azimuthal acoustic and longitudinal acoustic combination mode of the lamp.
A fourth form of the present invention is a first method for reducing vertical segregation in a high intensity discharge lamp. A current frequency signal is provided to the lamp, wherein the current frequency signal excites an azimuthal acoustic and longitudinal acoustic combination mode of the lamp. The current frequency signal is controlled to stabilize a reduction in vertical segregation in the lamp.
A fifth form of the present invention is a second method for reducing vertical segregation in a high intensity discharge lamp. A first current frequency sweep signal in the form of a square wave is provided. A second current frequency sweep signal in the form of a sine wave as a function of the first current frequency sweep signal is provided to the lamp, wherein the second current frequency sweep signal has a frequency range to excite an azimuthal acoustic and longitudinal acoustic combination mode of the lamp.
A sixth form of the present invention is a third method for reducing vertical segregation in a high intensity discharge lamp. A first current frequency sweep signal is provided to the lamp during a first time period, wherein the first current frequency sweep signal has a frequency range to stabilize an operation of the lamp. A current frequency signal is provided to the lamp during a second time period, wherein the second current frequency sweep signal excites an azimuthal acoustic and longitudinal acoustic combination mode of the lamp.
A seventh form of the present invention is a fourth method for reducing vertical segregation in a high intensity discharge lamp. A current frequency sweep signal is provided. A fixed current frequency signal is provided. A current frequency signal as a function of the fixed current frequency signal and the current frequency sweep signal is provided to the lamp, wherein the current frequency signal excites an azimuthal acoustic and longitudinal acoustic combination mode of the lamp.
The foregoing forms and other forms, features and advantages of the present invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the present invention rather than limiting, the scope of the present invention being defined by the appended claims and equivalents thereof.